1. Field of the Invention
The invention relates to the etching of aluminum electrolytic capacitor foil of a high cubic texture in an etching bath containing hydrochloric acid and aluminum chloride using direct current to produce a foil that has a significantly higher capacitance.
2. Description of the Prior Art
In the typical process of etching aluminum foil for use in electrolytic capacitors, an electrolytic bath containing sodium chloride or other salt and sulfate based electrolytes has been used. However, the capacitance of the resulting foil does not reach the high values which are achieved with the present invention.
U.S. Pat. No. 4,213,835 discloses a method for electrolytically etching a recrystalized aluminum foil which allows manufacture of foils with exclusively pure cylindrical or cubical etching tunnel structures and tunnel densities greater than 10.sup.7 /cm.sup.2 of foil surface. This process uses a potentiostatic etching technique. The problem with this technique is that it does not lend itself to large scale mass production of etched foils.
Still other processes have been used to yield a higher specific capacitance in aluminum foils. The present invention is directed to achieving a significant increase in specific capacitance for high volt foils.